The present invention relates generally to duct burner systems used with gas turbines and heat recovery steam generation (HRSG) systems. More specifically, the invention relates to duct burner systems and processes capable of burning low BTU (British thermal unit) fuel sources where variable geometric features and flow controls are applied to optimize the stoichiometry of a combustible mixture.
Many steel refineries, gasification plants, and other facilities producing low BTU fuels also use HRSG systems for heating and power transmission. In some cases, burning a low BTU fuel instead of a natural gas or other common high BTU fuel source may be classified as using renewable energy and economic credits may be realized. In addition, in some cases, the low BTU fuels may not otherwise be useful as fuel sources. Therefore, using low BTU fuels for supplemental firing in an HRSG system may prove beneficial from both an operational and economic standpoint.
However, using low BTU fuels for supplemental firing in an HRSG system may also prove problematic for several reasons. For instance, customization of the firing equipment may be required to satisfy the physical and chemical properties of the fuel for adequate combustion within flammability limits. In addition, the stoichiometric flow ratio may typically be uncontrolled in such supplemental firing systems.